The present invention relates to a coated powder, and more particularly relates to the coated powder that accomplishes natural coloring without deteriorating lightness when it is used as cosmetics or paints, and to a cosmetic prepared by blending the coated powder.
Conventionally, silica, titania dioxide or silica having a metal oxide such as titanium coated on the surface thereof has been known as pigments for cosmetics or paints. However, although titanium dioxide has high screening effect, there has been the problem that if it is used in a large amount, unnatural whiteness is obtained or lightness decreases, thereby it is difficult to obtain natural coloring.
The present invention has been made in view of the above circumstances, and has an object to provide a powder that accomplishes natural coloring without deteriorating lightness, and a cosmetic prepared by blending the same.
As a result of extensive investigations in view of the above existing circumstances, the present inventors have found that if a material having a refractive index of 1.9 to 3.1 is applied to a powder having a refractive index of 1.3 to 1.8 as a core, and a material having a refractive index of 1.3 to 1.8 is further applied thereto, linear transmission property of light at each wavelength can be freely adjusted by controlling a thickness of each coating layer; and since the total transmission amount can be maintained nearly 100% without substantially receiving influence of the coating thickness, when used as pigments for cosmetics, paints, or the like, a screening effect is not strong and lightness is not deteriorated, thereby natural coloring can be accomplished.
That is, the present invention provides a coated powder comprising (A) powder having a refractive index of 1.3 to 1.8 as a core, (B) a coating layer of a material having a refractive index of 1.9 to 3.1 on the powder (A), and (C) a coating layer of a material having a refractive index of 1.3 to 1.8 on the coating layer (B). The coated powder of the present invention enables linear transmittance of light to be adjusted according to the purpose of use, has a high total transmission amount of light, and does not substantially deteriorate lightness.
Further, the present invention provides a cosmetic prepared by blending the above-mentioned coated powder.
The present invention is described in detail below.
The coated powder of the present invention can be prepared by applying a material having a refractive index of 1.9 to 3.1 and a material having a refractive index of 1.3 to 1.8 to a powder having a refractive index of 1.3 to 1.8 as a core in that order with known methods such as a sol-gel method and a spray drying method.
The powder used as a core may have plate-like shape, spherical shape or indeterminate shape, but spherical shape is preferable in order to allow light to diffuse and transmit uniformly. Particle size of the powder used as a core may appropriately be adjusted depending on the conditions such as particle size of the desirable coated powder and weight ratio between the powder as a core and a material which is applied to the powder as a core as mentioned below. In general, the particle size of the powder as a core is preferably 0.05 to 45 xcexcm, and particularly preferably 0.3 to 28 xcexcm, although varying depending on the shape of the powder as a core. Further, the refractive index of the powder as a core is preferably 1.3 to 1.8, and particularly preferably 1.5 to 1.6. Examples of a material that can be used as the powder for a core include silica (refractive index n=about 1.54422), alumina (refractive index n=about 1.76-1.77), calcium carbonate (refractive index n=about 1.6585), and the like, and silica is preferable from the point of transmittance.
The material that is first applied to the powder as a core to form a first layer preferably has a refractive index of 1.9 to 3.1, and particularly preferably 2.1 to 2.6. Examples of the material that is first applied to the powder as a core to form a first layer include titania (refractive index n=about 2.493-2.586), zirconia (refractive index n=about 2.13, 2.19 or 2.20), and the like. The coating amount of this first layer can be adjusted depending on applications of the coated powder, but generally it may be about 1 to 50% by weight, and preferably about 5 to 30% by weight, based on the total amount of the coated powder. If the coating amount is less than 1% by weight, a screening effect is not sufficient, and if it exceeds 50% by weight, lightness lowers, which are not preferable.
The material that is further applied to the first layer on the core powder to form a second layer preferably has a refractive index of 1.3 to 1.8, and particularly preferably 1.5 to 1.6. Examples of the material for forming the second layer include silica, alumina, calcium carbonate, and the like, and the silica is preferable from the point of transmittance. The coating amount of this second layer can appropriately be adjusted depending on applications of the coated powder, but generally it may be about 1 to 30% by weight, and preferably about 2 to 10% by weight, based on the total amount of the coated powder. If the coating amount is less than 1% by weight, the total transmission amount of light decreases, and lightness does not increase, and even if it is applied in an amount exceeding 30% by weight, further improvement is not obtained in the effect of increasing lightness, which is not economical.
The coated powder of the present invention generally has a particle size of preferably 0.1 to 50 xcexcm, and particularly preferably 0.4 to 30 xcexcm, although depending on its shape. Even if the particle size is outside the above-mentioned range, the effect by the coated powder of the present invention can be obtained. However, if the particle size is within this range, it is easier to handle as pigments used for cosmetics, paints, or the like, and when it is blended into cosmetics, texture when applied is better.
In order to obtain such a coated powder, for example, an alkoxysilane is subjected to hydrolysis by addition of ammonia to produce spherical silica particles, the particles are then introduced into a titianium alkoxide solution, and hydrolysis is conducted to form a coating layer of hydrolyzate of titanium alkoxide on the surface, followed by burning, or the like, thereby forming a coating layer as the first layer. This coated powder is further introduced into an alkoxysilane solution, the alkoxysilane is hydrolyzed to form the second layer, followed by burning, thereby producing the coated powder of the present invention. Formation of the second layer can also be conducted by a method in which an alkoxysilane solution is sprayed to the powder having the first layer, then the obtained powder is heated and dried. Further, commercially available silica powder can be used as the powder of starting material. For example, true spherical silica powder produced by the process described in Japanese Patent Application Laid-open No. 61-270201 and the like are exemplified.
The coated powder of the present invention can be blended into cosmetics, paints, or the like. The blending amount of the coated powder may be appropriately adjusted depending on the purpose of cosmetics, paints, or the like.
In the cosmetic of the present invention containing the above-mentioned coated powder, form and application thereof are not particularly limited, and the form may be, for example, a solution-form, a milky lotion-form, a cream-form, an aqueous gel-form or the like. The application thereof includes foundation, control color, make-up base, eye color, face lotion, face milky lotion, cheek color, lip color, and the like. In addition to the above-mentioned coated powder, the cosmetic of the present invention can contain various components generally used in cosmetics such as aqueous component, oily component, surface active agent, moisturizer, thickener, coloring material, perfume, antioxidant, pH modifier, chelating agent, preservative, ultraviolet inhibitor, anti-inflammatory agent, whitening agent and powder other than the coated powder of the present invention.
The cosmetic of the present invention can be prepared in the same manner as in the ordinary cosmetics except for blending the coated powder.
The coated powder of the present invention is explained by referring to the following examples.